This invention relates generally to computer data storage and video display equipment. More particularly, the invention relates to an apparatus for effecting the storage of computer generated digital information and analog video information using a video recording device such as a video tape recorder, VCR, or the like. Further, the invention relates to an apparatus for displaying video and television signals on a computer CRT monitor.
Present day computer systems employ architectures which provide for the storage of digital information by a number of different mechanisms, each having certain advantages and disadvantages. At the center of most computer systems is the central processing unit or CPU which interprets, processes and executes instructions (computer programs). The CPU coordinates the cooperation of various other elements of the computer system and also oversees the input/output procedures whereby the computer system communicates with peripheral devices. The instructions or computer programs which the central processing unit executes are stored in some form of memory device where they may be accessed by the CPU upon demand. These instructions are digital information usually comprising a plurality of binary digits or bits arranged into groups, commonly called bytes or words. In addition to executing instructions, the CPU also generates digital information also as groups of binary digits. The digital information so generated may represent additional computer instructions to be executed by the CPU or by some other processing unit, or the digital information may represent data to be stored, acted upon or displayed. Text files produced by word processing programs and source code computer program listings written in higher level computer languages are two examples of such data.
In order to store digital information, whether it represents computer instructions or data, so that the CPU can access it, and process and manipulate it quickly, random access memory (RAM) is included as a part of the computer system. Random access memory comprises an array of individually addressable electronic data cells, each capable of storing one biary digit or bit. Ordinarily these data cells are arranged in groups corresponding to the byte or word format of the digital information to be stored therein. One advantage of RAM memory is that digital information can be stored or retrieved very rapidly. One disadvantage of present day RAM is that it does not retain stored digitial information when electrical power is interrupted. Because of this disadvantage with RAM memory, most computer systems also employ an alternate form of data storage, usually some form of magnetic data storage (floppy disks, fixed disks or hard disks, and the like). Such magnetic data storage media have the advantage of being able to store digital information magnetically, so that a constant supply of electrical power is not required.
One disadvantage of magnetic data storage systems is that the magnetic media are vulnerable to contamination by dirt, dust and other foreign materials. In the case of the hard disk or fixed disk system, this vulnerability to foreign contaminants is particularly acute since such systems employ rapidly rotating disks (3,000 rpm) and read/write heads positioned less than the thickness of a human hair above the surface of the disk. Even minute foreign particles, such as a single human hair, can cause the read/write head to bounce and crash into the disk surface, causing permanent damage almost instantaneously. Because of such vulnerability to contaminants it is considered wise practice to make duplicate or back-up copies of the stored data. In the case of floppy disk systems, a second diskette may be recorded to serve as a back-up copy. With hard disks, on the other hand, it has not proven practical to make back-up copies using additional hard disk storage devices, due to the relatively high cost of additional hard disk devices. Similarly, it has not proven practical to record back-up copies of a hard disk memory onto floppy diskettes, since a typical ten megabyte hard disk memory would require some thirty to forty or more individual floppy diskettes in order to provide a full back-up copy.
Due to the impracticality of using floppy diskettes to back-up hard disk memory systems, some hard disk systems include provisions for making back-up copies in serial format on cassette tapes, known as tape streamers. With such tape streamer systems the digital information is stored directly, in serial form, as a continuous sequence or stream of bits. Such tape streamer systems are comparatively quite expensive. In addition to tape streamers, there have been proposed other systems for producing back-up copies using audio and video cassette tape recording systems.
A common problem with all tape back-up systems, digital tape streamers, audio cassettes and video cassettes alike, is that the digital information serially stored on such devices may not be randomly accessed and viewed by the human operator. The human operator cannot browse through the contents of the back-up copy as one might browse through chapter headings of a book, since these back-up systems do not provide any human readable information. While most computer systems employ a video monitor for displaying human readable information, these back-up systems of the prior art cannot convey video information to such video monitors directly while the back-up tape is being replayed.
The present invention overcomes these shortcomings by providing a computer memory back-up system which permits the storage of both digital information (computer instructions and digital data) as well as analog video information using a single video recording apparatus, such as a video tape recorder, VCR, or the like. Using the invention, the computer operator can back-up the entire computer memory, or only selected files or blocks of computer memory, while at the same time recording analog video information that may be played back directly by the computer's video monitor or an auxiliary monitor or television set without further processing by the computer's central processing unit. The video analog information may, for example, comprise an informative header conveying human readable information about the digital data stored elsewhere in the video recording device.
The invention greatly simplifies producing back-up copies of computer data files or programs by permitting the operator to record a human readable file header describing the data file or program to follow. The computer operator is thus able to browse through the contents of the information stored in the video recording device, to locate a particular file or program or to make changes to that file or program without affecting other data stored elsewhere in the video recording device.
The invention supports the broad capability of recording and displaying any type of analog video information, not just human readable text. For example, graphic information including both still and motion pictures may be integrated with digital information upon the same recording medium. Because the analog video information can be directly displayed using the computer's video monitor or an auxiliary monitor or television set without manipulation by the central processing unit, the video information enjoys an inherently much higher resolution than computer graphics. Photographs, motion pictures, blueprints and other visual information can be read and stored in analog form using video television cameras or the like without the need to digitize the information to make it computer compatible. Furthermore, the invention also supports the capability to display video or television signals directly upon the computer CRT monitor. This feature may be used, for example, to display prerecorded tape or braodcast television, or live television on the CRT monitor--for training sessions, interoffice communication or the like.
In accordance with the invention, an apparatus for storing and retrieving digital and analog information using a video recording device having a means for serially storing video information is provided. The invention is intended for use with a computer system having a central processing unit for processing digital information through a parallel data channel and further having a video output means responsive to the central processing unit for generating analog information and for generating video sync signals. The invention comprises a parallel to serial conversion means coupled to the parallel data channel to receive the digital information and to provide the digital information in serial form. A signal processing means is receptive of the analog information and video sync signals and is further coupled to the conversion means to receive the digital information. The signal processing means selectively provides to the video recording device either a first video signal or a second video signal. The first video signal comprises the composite of the analog information and the video sync signals while the second video signal comprises the composite of the digital information and the video sync signals. In this fashion, both analog information and digital information may be stored upon the serial storage medium of the video recording device.
When used in conjunction with a video monitor, such as a video monitor resonsive to the analog information and video sync signals generated by the computer system, e.g., the computer video monitor, the invention has the capability of directing analog video information directly to the video monitor without further processing by the central processing unit. In accordance with the invention a signal directing means controlled by the central processing unit and receptive of the serially stored video information from the video recording device is provided. The signal directing means is further receptive of analog information and video sync signals from the video output means of the computer system. The signal directing means is coupled to the video monitor for selectively directing to the video monitor either the serially stored video information from the recording device or the analog information and video sync signals from the computer system, thereby permitting the visual display of both sources of information upon the same video monitor.
In the preferred embodiment the invention is adapted to plug into one of the computer systems peripheral expansion slots, so that it may be housed entirely within the computer cabinet. The invention thus takes up no valuable desk top space and is capable of deriving electrical power directly from the computer system power supply through the expansion slot. The invention further comprises firmware storage of all computer instructions needed to assist the central processing unit in interfacing with the invention automatically. Such instructions make it possible for the invention to determine what type of computer system it is connected to and also the computer memory address or addresses where programs or data to be saved presently reside.
The invention further includes means for extracting video sync signals directly from the video output circuit within the computer system to insure compatability and also to make most efficient use of existing hardware without duplication. A mixing circuit is receptive of the serialized digital information from the signal processing means and also receptive of the extracted video sync signals. The mixing circuit provides a data video signal comprising digital information and video sync signals in a predetermined relationship, providing data video signals which are compatable with the storage format of the video recording device.
The invention further provides automatic search capabilities, whereby digital information can be stored and retrieved at a predetermined location on the video recording medium. A means is provided for converting the digital information into video information so that the information may be stored on the video recording medium. A means is also provided converting the serially stored video information into digital information, so that it may be processed by the computer system. In addition, a means for encoding a plurality of serially spaced markers on the recording medium is provided. Each marker corresponds to a different storage location on the medium. A control means responsive to the central processing unit and also responsive to the markers controls the video recording device causing it to position the recording medium at a location prescribed by the computer system. When a video tape recorder is used as the video recording device, the markers may be encoded on the audio recording track of the video tape, using a self-clocking code such as the Manchester code or the equivalent. If necessary, a video tape recorder may require modification to permit the audio read/write head to remain in contact with or in close proximity to the recording medium when the video recorder is operating in fast forward or fast reverse modes. The automatic search function permits the computer, acting through the interface apparatus of the invention, to search for a particular location on the tape or recording medium at fast forward or fast reverse speeds, and then to automatically commence recording or playback at normal recording and playback speeds. The automatic search feature thereby allows the computer to locate a desired data file quickly and automatically.
These and other objects and advantages of the invention will become more apparent from a review of the following specification and with reference to the accompanying drawings.